FSRTL_PER_STREAM_CONTEXT structure (ntifs.h)
The FSRTL_PER_STREAM_CONTEXT structure contains context information that a file system filter driver maintains about a file stream.
Syntax
typedef struct _FSRTL_PER_STREAM_CONTEXT {
LIST_ENTRY Links;
PVOID OwnerId;
PVOID InstanceId;
PFREE_FUNCTION FreeCallback;
} FSRTL_PER_STREAM_CONTEXT, *PFSRTL_PER_STREAM_CONTEXT;
Members
Links
Link for this structure in the list of all per-stream context structures associated with the same file stream. FsRtlInsertPerStreamContext inserts this member into the list of all per-stream context structures for a file stream. To get a pointer to the head of the list from a file object, use the FsRtlGetPerStreamContextPointer macro, and cast the result to a PFSRTL_ADVANCED_FCB_HEADER pointer. The list pointer is the FilterContexts member in the advanced file control block (FCB) header structure for the file stream.
OwnerId
Pointer to a filter-driver-allocated variable that uniquely identifies the owner of the per-stream context structure. The format of this variable is filter-driver-specific. Filter writers should choose a value that is both meaningful and convenient, such as the address of a driver object or device object. Filter drivers must set this member to a non-NULL value.
InstanceId
Pointer to a filter-driver-allocated variable that can be used to distinguish among per-stream context structures created by the same filter driver. The format of this variable is filter-driver-specific. Filter writers should choose a value that is both meaningful and convenient, such as the address of the stream context object for the file stream. (To get this address from a file object, use the FsRtlGetPerStreamContextPointer macro.)
This member is optional and can be NULL.
FreeCallback
Pointer to a callback routine that frees the per-stream context structure. This routine and its parameters are defined as follows:
VOID
(*PFREE_FUNCTION) (
IN PVOID Buffer
);
Buffer
Pointer to the FSRTL_PER_STREAM_CONTEXT structure to free.
Remarks
File system filter drivers can use a FSRTL_PER_STREAM_CONTEXT structure to maintain context information for a file stream. This structure can be used as is or embedded in a driver-defined, per-stream context structure.
When a file system tears down the stream context object for a file stream, it must call FsRtlTeardownPerStreamContexts, which in turn calls the FreeCallback routines of all per-stream context structures associated with the file stream.
The FsRtlSupportsPerStreamContexts macro determines whether a file system supports per-stream contexts for a given file stream.
BOOLEAN FsRtlSupportsPerStreamContexts(
[in] PFILE_OBJECT FileObject
);
Parameters
FileObject [in]
PFILE_OBJECT
A pointer to a file object for the file stream.
Return value
BOOLEAN
The FsRtlSupportsPerStreamContexts macro returns TRUE if the file system supports per-stream contexts for the file stream, FALSE otherwise.
File system filter drivers call FsRtlSupportsPerStreamContexts to determine whether the underlying file system supports per-stream contexts for the file stream represented by a given file object. Note that a file system might support per-stream contexts for some types of files but not for others. For example, NTFS and FAT do not currently support per-stream contexts for paging files.
For more information, see Tracking Per-Stream Context in a Legacy File System Filter Driver.
Requirements
| Requirement | Value |
|---|---|
| Minimum supported client | This structure is Windows XP |
| Header | ntifs.h (include Ntifs.h) |
See also
FsRtlGetPerStreamContextPointer
FsRtlTeardownPerStreamContexts
Tracking Per-Stream Context in a Legacy File System Filter Driver